1. Field of the Invention
The invention generally relates to a fuel injector and, more particularly, to a dampened stop pin that reduces the closing speed of the needle prior to seating at a needle seat to block the passage of fuel out of the nozzle spray holes.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current designs, a driver delivers a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid shifts a spool into the open position so as to align grooves or orifices (hereinafter referred to as “grooves”) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high-pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high-pressure plunger chamber. As the pressure in the high-pressure plunger chamber increases, the fuel pressure will begin to rise above a valve opening pressure. At the prescribed fuel pressure level, the needle will shift against the stop pin and the biasing force of the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.
It is desirable to provide rapid closing of the needle after a fuel injection event in order to limit undesirable noise and improve engine emissions. The needle spring, however, contains a high mechanical load force when fully opened. As a result, closing the needle at a relatively high speed causes the needle to strike the needle seat proximate the nozzle tip with great force. Such an impact can severely damage the needle or may even cause the nozzle body to crack.